Escherichia coli (E. coli) is a gram negative bacterium which occurs naturally in the intestinal tract of warm-blooded animals. The presence of this organism is a reliable indicator of fecal contamination. If E. coli bacterium is present in a given sample of material such as water, fecal matter, etc., it is also possible that Salmonella, Shigella, Vibrio, enteric viruses, and intestinal parasites are also present in the sample.
No process is presently known whereby the presence of E. coli can be reliably detected merely by growing the organism in or on a specific medium. Current processes used to detect and identify this microorganism involve visual inspection of pure culture colonies, and a series of subsequent biochemical tests.
The present process involves the usual initial or preliminary steps of isolating individual bacteria known in microbiology. In such processes, agar containing added nutrients is a common support media employed in the culturing of microorganisms for the purpose of isolating and identifying individual bacteria. A method of isolating individual bacteria involves culturing microorganisms on agar plates. This process involves streaking the surface of an agar plate (a Petri-dish containing agar fortified with nutrients) with a sample containing different microorganisms. The individual organisms are deposited along the track of the streak. Thereafter the agar plate is incubated at selected temperatures for a period of time. The individual organisms grow in colonies along the track of the streak and may be further isolated by subculturing, i.e., taking a sample from a particular colony which is partially contaminated and repeating the process with another agar plate.
In the present invention, after a pure culture is isolated, it is placed in the medium of this invention, and if it is E. coli, a change occurs in the broth which identifies the organism to the observer as E. coli.
We have discovered a medium which will selectively identify E. coli. This medium will yield relatively few positive results in the presence of Klebsiella or Enterobacter. The essential ingredient of this medium is coumaric acid, preferably para-coumaric acid. The ortho - and meta - forms of coumaric acid also are effective, but are less reliable whereas the para form effectively inhibits nearly all fecal coliform organisms except E. coli.